1. Field of the Invention
The present invention relates in general to earth-boring bits, particularly to those having rotatable cutters in which seal assemblies retain lubricant within the bearing areas.
2. Background Information
One of the most successful seal means used in earth-boring bits of the type having rotatable cutters is the O-ring seal disclosed in commonly assigned U.S. Pat. No. 3,397,928, to Galle. The o-ring seal successfully confines lubricant to the bearing area while excluding detritus for long periods of time before failure.
A more recent seal development is the rigid or metal face seal. In the rigid face seal type, the seal interface is between one or two rigid, usually steel, seal rings. One or two elastomer o-rings serve to energize or urge the seal faces of the rigid ring or rings in contact with each other. The rigid face seal has proved to be as successful as the o-ring seal and provides an improved ability to accommodate pressure fluctuations in the bit lubricant.
A somewhat less successful design is the Belleville seal, in which elastomer elements are bonded to a rigid metallic ring or washer, which is placed under compression in the seal gland and the elastomer elements perform the bulk of the sealing.
All three types of seals are subject to the condition known as mud packing. This condition occurs when the solid matter in drilling fluid or mud is carried into the seal gland, where it adheres to gland and/or seal component surfaces and causes deformation and/or slippage of elastomeric seal components. Moreover, these particles can accelerate abrasive wear of all seal components.
A need exists for seal assemblies that supplement the main bearing seal by assisting in the prevention of entry of debris into the seal assembly itself.